Mechanical surface treatments cold-work the surface material, causing compressive residual stresses and, depending on the properties of the materials, often strengthening the surface against strain. One of the most common and versatile of the cold-working treatments is “shot peening.” In shot peening, the surface is bombarded with high-velocity shot, round metallic, glass or ceramic beads, discharged from a pneumatic nozzle. The resulting lightly hammered or “peened” effect places the surface in residual, preferably uniform, compression.
In one aspect, embodiments disclosed herein relate to a fluid end having a longitudinal bore less than about 36 inches in diameter, the longitudinal bore having an internal surface that is cold-worked to have compressive stresses of at least 15 ksi (103.42 MPa) beneath the metal surface up to about 40 mils (1.016 mm).
In other aspects, embodiments disclosed herein relate to a fluid end having a longitudinal bore less than about six inches in diameter, the longitudinal bore having an internal surface having a lip that is cold-worked to have compressive stresses of at least 100 ksi (689.48 MPa) beneath the metal surface of at least a portion of the lip up to about 1 mil.
In yet other aspects, embodiments disclosed herein relate to a fluid end having a longitudinal bore less than about six inches in diameter, the longitudinal bore having an internal surface having a lip comprising a peened coverage of at least about one hundred percent (100%) provided over at least fifty percent (50%) of the surface of the lip.